Fountain solution thickness measurement using optical properties of solidified fountain solution in a lithography printing system

ABSTRACT

According to aspects of the embodiments, there is provided a method of measuring the amount of fountain solution employed in a digital offset lithography printing system. Fountain solution thickness is measured using a glass roll at a lower temperature than the fountain solution. The lower temperature causes the fountain solution to undergo a change in state and in a solid state the fountain solution crystalizes and changes roll opacity with the thickness of the film. When radiated with a light source the opacity is continuously measured through the surface of the roller. The thickness of the crystallized fountain solution can then be determined via the opacity level increase by the crystallization and the impact to the opacity on the glass roll.

FIELD OF DISCLOSURE

This invention relates generally to digital printing systems, and moreparticularly, to fountain solution deposition systems and methods formeasuring the thickness of the fountain solution.

BACKGROUND

Conventional lithographic printing techniques cannot accommodate truehigh speed variable data printing processes in which images to beprinted change from impression to impression, for example, as enabled bydigital printing systems. The lithography process is often relied upon,however, because it provides very high quality printing due to thequality and color gamut of the inks used. Lithographic inks are alsoless expensive than other inks, toners, and many other types of printingor marking materials.

Ink-based digital printing uses a variable data lithography printingsystem, or digital offset printing system, or a digital advancedlithography imaging system. A “variable data lithography system” is asystem that is configured for lithographic printing using lithographicinks and based on digital image data, which may be variable from oneimage to the next. “Variable data lithography printing,” or “digitalink-based printing,” or “digital offset printing,” or digital advancedlithography imaging is lithographic printing of variable image data forproducing images on a substrate that are changeable with each subsequentrendering of an image on the substrate in an image forming process.

For example, a digital offset printing process may include transferringink onto a portion of an imaging member (e.g., fluorosilicone-containingimaging member, imaging blanket, printing plate) that has beenselectively coated with a fountain solution (e.g., dampening fluid)layer according to variable image data. According to a lithographictechnique, referred to as variable data lithography, a non-patternedreimageable surface of the imaging member is initially uniformly coatedwith the fountain solution layer. An imaging system then evaporatesregions of the fountain solution layer in an image area by exposure to afocused radiation source (e.g., a laser light source, high power laser)to form pockets. A temporary pattern latent image in the fountainsolution is thereby formed on the surface of the digital offset imagingmember. The latent image corresponds to a pattern of the appliedfountain solution that is left over after evaporation. Ink appliedthereover is retained in the pockets where the laser has vaporized thefountain solution. Conversely, ink is rejected by the plate regionswhere fountain solution remains. The inked surface is then brought intocontact with a substrate at a transfer nip and the ink transfers fromthe pockets in the fountain solution layer to the substrate. Thefountain solution may then be removed, a new uniform layer of fountainsolution applied to the printing plate, and the process repeated.

Digital printing is generally understood to refer to systems and methodsof variable data lithography, in which images may be varied amongconsecutively printed images or pages. “Variable data lithographyprinting,” or “ink-based digital printing,” or “digital offset printing”are terms generally referring to printing of variable image data forproducing images on a plurality of image receiving media substrates, theimages being changeable with each subsequent rendering of an image on animage receiving media substrate in an image forming process. “Variabledata lithographic printing” includes offset printing of ink imagesgenerally using specially-formulated lithographic inks, the images beingbased on digital image data that may vary from image to image, such as,for example, between cycles of an imaging member having a reimageablesurface.

The inventors have found that the amount or thickness of the fountainlayer which is present on the printing plate is a critical part ofdigital offset printing methods in order to maintain sharp and clearimages. The layer is extremely thin, on the order of tens of nanometers,which until now any direct measurement of its thickness difficult.Knowledge of the layer thickness is helpful to control the system imagequality. For example, if insufficient fountain solution is provided to anon-image area, the ink will invade the non-image area to create adistorted printing image. Conversely, if too much fountain solution isprovided so that the fountain solution enters the image area, adistortion of the image will also result.

The amount or thickness of fountain solution which is applied to theprinting plates is therefore critical to the production of clear printedimages. Currently, the amount of fountain solution which is applied tothe plates used in offset lithography is based principally on theexperience of the offset press operator. There is to date no accuratemethod of quantifying the amount of fountain solution used in offsetlithography printing processes so as to minimize the undesirable effectsof too much or too little fountain solution.

It would therefore be a significant advance in the art of digital offsetprinting if the amount of fountain solution which is used in the markingprocess could be quantified without disrupting the operation of theprinting process.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects of one or more embodiments or examples ofthe present teachings. This summary is not an extensive overview, nor isit intended to identify key or critical elements of the presentteachings, nor to delineate the scope of the disclosure. Rather, itsprimary purpose is merely to present one or more concepts in simplifiedform as a prelude to the detailed description presented later.Additional goals and advantages will become more evident in thedescription of the figures, the detailed description of the disclosure,and the claims.

The foregoing and/or other aspects and utilities embodied in the presentdisclosure may be achieved by providing a fountain solution thicknessmeasurement system. The measurement system for thin liquid film, such asfountain solution, uses optical properties of a phase changed film todetermine the thickness of the fountain solution.

The propose fountain solution thickness measurement system using opticalproperties of solidified fountain solution film. It is further proposedto transfer a concentration of the fountain solution from an imagingblanket to a clear or glass roller with an engineered surface of knownsurface roughness. Further, the fountain solution layer is evaporated orfrozen into a solid state that can then be measured for opacity by anemissive light source and sensor.

According to aspects illustrated herein, an exemplary method to measurefountain solution thickness for variable data lithography printingcomprising using an engineered surface with an opacity that varies as afunction of fountain solution thickness; using an emissive light sourceto pass a light along a path from the source through the engineeredsurface; receiving light passing through the engineered surface at alight detector; generating a signal proportional to the opacity level ofthe engineered surface from the light impinging on the light detector;and determining the thickness of the fountain solution on the engineeredsurface from the opacity level.

According to aspects described herein, a system useful for printing withan ink-based digital image forming device comprising a processor; and astorage device coupled to the processor, wherein the storage devicecomprises instructions which, when executed by the processor, cause theprocessor to control fountain solution deposition process maintainfountain solution at a set thickness for variable data lithographyprinting by: using an engineered surface with an opacity that varies asa function of fountain solution thickness; using an emissive lightsource to pass a light along a path from the source through theengineered surface; receiving light passing through the engineeredsurface at a light detector; generating a signal proportional to theopacity level of the engineered surface from the light impinging on thelight detector; determining the thickness of the fountain solution onthe engineered surface from the opacity level; and controlling thefountain solution deposition process based on the determined thicknessof the fountain solution.

Exemplary embodiments are described herein. It is envisioned, however,that any system that incorporates features of apparatus and systemsdescribed herein are encompassed by the scope and spirit of theexemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the disclosed apparatuses, mechanismsand methods will be described, in detail, with reference to thefollowing drawings, in which like referenced numerals designate similaror identical elements, and:

FIG. 1 is block diagram of a digital image forming device in accordancewith examples of the embodiments;

FIG. 2 shows a schematic view of a clear glass roll with internalemissive lighting system to illuminate solidified fountain solution onsurface of roller in accordance to an embodiment;

FIG. 3 is part of a digital image forming device that includes afeedback loop for controlling and applicator that dispenses fluidsolution in accordance to an embodiment;

FIG. 4 is a block diagram of a controller with a processor for executinginstructions to automatically control devices in the digital imageforming device depicted in FIGS. 1-3 in accordance to an embodiment;

FIG. 5 shows transferring fountain solution by evaporation from theimaging blanket to the clear glass roll for fountain solutionmeasurement in accordance to an embodiment;

FIG. 6 is a plot of opacity as a function of thickness of the solidifiedfountain solution in accordance to an embodiment; and

FIG. 7 is a flowchart depicting the operation of an exemplary method todirectly measure fountain solution for use in a digital image formingdevice.

DETAILED DESCRIPTION

Illustrative examples of the devices, systems, and methods disclosedherein are provided below. An embodiment of the devices, systems, andmethods may include any one or more, and any combination of, theexamples described below. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth below. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Accordingly, the exemplary embodiments are intended to cover allalternatives, modifications, and equivalents as may be included withinthe spirit and scope of the apparatuses, mechanisms and methods asdescribed herein.

We initially point out that description of well-known startingmaterials, processing techniques, components, equipment and otherwell-known details may merely be summarized or are omitted so as not tounnecessarily obscure the details of the present disclosure. Thus, wheredetails are otherwise well known, we leave it to the application of thepresent disclosure to suggest or dictate choices relating to thosedetails. The drawings depict various examples related to embodiments ofillustrative methods, apparatus, and systems for inking from an inkingmember to the reimageable surface of a digital imaging member.

When referring to any numerical range of values herein, such ranges areunderstood to include each and every number and/or fraction between thestated range minimum and maximum. For example, a range of 0.5-6% wouldexpressly include the endpoints 0.5% and 6%, plus all intermediatevalues of 0.6%, 0.7%, and 0.9%, all the way up to and including 5.95%,5.97%, and 5.99%. The same applies to each other numerical propertyand/or elemental range set forth herein, unless the context clearlydictates otherwise.

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (forexample, it includes at least the degree of error associated with themeasurement of the particular quantity). When used with a specificvalue, it should also be considered as disclosing that value. Forexample, the term “about 2” also discloses the value “2” and the range“from about 2 to about 4” also discloses the range “from 2 to 4.”

The term “controller” is used herein generally to describe variousapparatus such as a computing device relating to the operation of one ormore device that directs or regulates a process or machine. A controllercan be implemented in numerous ways (e.g., such as with dedicatedhardware) to perform various functions discussed herein. A “processor”is one example of a controller which employs one or more microprocessorsthat may be programmed using software (e.g., microcode) to performvarious functions discussed herein. A controller may be implemented withor without employing a processor, and also may be implemented as acombination of dedicated hardware to perform some functions and aprocessor (e.g., one or more programmed microprocessors and associatedcircuitry) to perform other functions. Examples of controller componentsthat may be employed in various embodiments of the present disclosureinclude, but are not limited to, conventional microprocessors,application specific integrated circuits (ASICs), and field-programmablegate arrays (FPGAs).

The terms “media”, “print media”, “print substrate” and “print sheet”generally refers to a usually flexible physical sheet of paper, polymer,Mylar material, plastic, or other suitable physical print mediasubstrate, sheets, webs, etc., for images, whether precut or web fed.The listed terms “media”, “print media”, “print substrate” and “printsheet” may also include woven fabrics, non-woven fabrics, metal films,and foils, as readily understood by a skilled artisan.

The term “image forming device”, “printing device” or “printing system”as used herein may refer to a digital copier or printer, scanner, imageprinting machine, xerographic device, electrostatographic device,digital production press, document processing system, image reproductionmachine, bookmaking machine, facsimile machine, multi-function machine,or generally an apparatus useful in performing a print process or thelike and can include several marking engines, feed mechanism, scanningassembly as well as other print media processing units, such as paperfeeders, finishers, and the like. A “printing system” may handle sheets,webs, substrates, and the like. A printing system can place marks on anysurface, and the like, and is any machine that reads marks on inputsheets; or any combination of such machines.

The term “fountain solution” or “dampening fluid” refers to dampeningfluid that may coat or cover a surface of a structure (e.g., imagingmember, transfer roll) of an image forming device to affect connectionof a marking material (e.g., ink, toner, pigmented or dyed particles orfluid) to the surface. The fountain solution may include wateroptionally with small amounts of additives (e.g., isopropyl alcohol,ethanol) added to reduce surface tension as well as to lower evaporationenergy necessary to support subsequent laser patterning. Low surfaceenergy solvents, for example volatile silicone oils, can also serve asfountain solutions. Fountain solutions may also include wettingsurfactants, such as silicone glycol copolymers. The fountain solutionmay include D4 or D5 dampening fluid alone, mixed, and/or with wettingagents. The fountain solution may also include Isopar G, Isopar H,Dowsil OS20, Dowsil OS30, and mixtures thereof.

As used herein, the term “opacity” is intended to be a broad term thatmeans the ability to block the transmission of radiant energy, e.g.,light energy, and less than all or all. Or at least a substantialportion of the structure and configuration that absorbs or otherwiseblocks light.

Inking systems or devices may be incorporated into a digital offsetimage forming device architecture so that the inking system is arrangedabout a central imaging plate, also referred to as an imaging member. Insuch a system, the imaging member, including a central drum or cylinderis provided with a reimageable layer. This blanket layer has specificproperties such as composition, surface profile, and so on so as to bewell suited for receipt and carrying a layer of a fountain solution. Asurface of the imaging member is reimageable making the imaging member adigital imaging member. The surface is constructed of elastomericmaterials and conformable. A paper path architecture may be situatedadjacent the imaging member to form a media transfer nip.

A layer of fountain solution may be applied to the surface of theimaging member by a dampening system. In a digital evaporation step,particular portions of the fountain solution layer applied to thesurface of the imaging member may be evaporated by a digital evaporationsystem. For example, portions of the fountain solution layer may bevaporized by an optical patterning subsystem such as a scanned,modulated laser that patterns the fluid solution layer to form a latentimage. In a vapor removal step, the vaporized fountain solution may becollected by a vapor removal device or vacuum to prevent condensation ofthe vaporized fountain solution back onto the imaging plate.

In an inking step, ink may be transferred from an inking system to thesurface of the imaging member such that the ink selectively resides inevaporated voids formed by the patterning subsystem in the fountainsolution layer to form an inked image. In an image transfer step, theinked image is then transferred to a print substrate such as paper viapressure at the media transfer nip.

In a variable lithographic printing process, previously imaged ink mustbe removed from the imaging member surface to prevent ghosting. After animage transfer step, the surface of the imaging member may be cleaned bya cleaning system so that the printing process may be repeated. Forexample, tacky cleaning rollers may be used to remove residual ink andfountain solution from the surface of the imaging member. The inking,transferring, and cleaning process causes the properties of the imagingmember or imaging blanket to undergo wear and tear causing changesthrough the life of the blanket. Property changes of the blanket createa huge variability that makes thin film thickness measurement adifficult or daunting task.

FIG. 1 depicts an exemplary ink-based digital image forming device 10.The image forming device 10 may include dampening station 12 havingfountain solution applicator 14, optical patterning subsystem 16, inkingapparatus 18, and a cleaning device 20. The image forming device 10 mayalso include one or more rheological conditioning subsystems 22 asdiscussed, for example, in greater detail below. FIG. 1 shows thefountain solution applicator 14 arranged with a digital imaging member24 having a reimageable surface 26. While FIG. 1 shows components thatare formed as rollers, other suitable forms and shapes may beimplemented.

The imaging member surface 26 may be wear resistant and flexible. Thesurface 26 may be reimageable and conformable, having an elasticity anddurometer, and sufficient flexibility for coating ink over a variety ofdifferent media types having different levels of roughness. A thicknessof the reimageable surface layer may be, for example, about 0.5millimeters to about 4 millimeters. The surface 26 should have a weakadhesion force to ink, yet good oleophilic wetting properties with theink for promoting uniform inking of the reimageable surface andsubsequent transfer lift of the ink onto a print substrate.

The soft, conformable surface 26 of the imaging member 24 may include,for example, hydrophobic polymers such as silicones, partially or fullyfluorinated fluorosilicones and FKM fluoroelastomers. Other materialsmay be employed, including blends of polyurethanes, fluorocarbons,polymer catalysts, platinum catalyst, hydrosilyation catalyst, etc. Thesurface may be configured to conform to a print substrate on which anink image is printed. To provide effective wetting of fountain solutionssuch as water-based dampening fluid, the silicone surface need not behydrophilic, but may be hydrophobic. Wetting surfactants, such assilicone glycol copolymers, may be added to the fountain solution toallow the fountain solution to wet the reimageable surface 26. Theimaging member 24 may include conformable reimageable surface 26 of ablanket or belt wrapped around a roll or drum. The imaging membersurface 26 may be temperature controlled to aid in a printing operation.For example, the imaging member 24 may be cooled internally (e.g., withchilled fluid) or externally (e.g., via a blanket chiller roll 28 to atemperature (e.g., about 10° C.-60° C.) that may aid in the imageforming, transfer and cleaning operations of image forming device 10.

The reimageable surface 26 or any of the underlying layers of thereimageable belt/blanket may incorporate a radiation sensitive fillermaterial that can absorb laser energy or other highly directed energy inan efficient manner. Examples of suitable radiation sensitive materialsare, for example, microscopic (e.g., average particle size less than 10micrometers) to nanometer sized (e.g., average particle size less than1000 nanometers) carbon black particles, carbon black in the form ofnano particles of, single or multi-wall nanotubes, graphene, iron oxidenano particles, nickel plated nano particles, etc., added to the polymerin at least the near-surface region. It is also possible that no fillermaterial is needed if the wavelength of a laser is chosen so to match anabsorption peak of the molecules contained within the fountain solutionor the molecular chemistry of the outer surface layer. As an example, a2.94 μm wavelength laser would be readily absorbed due to the intrinsicabsorption peak of water molecules at this wavelength.

The fountain solution applicator 14 may be configured to deposit a layerof fountain solution onto the imaging member surface 26 directly or viaan intermediate member (e.g., roller 30) of the dampening station 12.While not being limited to particular configuration, the fountainsolution applicator 14 may include a series of rollers or sprays (notshown) for uniformly wetting the reimageable surface 26 with a uniformlayer of fountain solution with the thickness of the layer beingcontrolled. The series of rollers may be considered as dampening rollersor a dampening unit, for uniformly wetting the reimageable surface 26with a layer of fountain solution. The fountain solution may be appliedby fluid or vapor deposition to create a thin layer (e.g., between about0.01 μm and about 1.0 μm in thickness, less than 5 μm, about 50 nm to100 nm) of the fountain solution for uniform wetting and pinning.

A sensor 32, for example an in-situ non-contact laser gloss sensor orlaser contrast sensor, may be used to confirm the uniformity of thelayer. Such a sensor can be used to automate the dampening station 12.While not being limited to a particular utility, the sensor 32 mayprovide feedback to control the deposition of the fountain solution ontoreimageable surface 26.

The optical patterning subsystem 16 is located downstream the fountainsolution applicator 14 in the printing processing direction toselectively pattern a latent image in the layer of fountain solution byimage-wise patterning using, for example, laser energy. For example, thefountain solution layer is exposed to an energy source (e.g. a laser)that selectively applies energy to portions of the layer to image-wiseevaporate the fountain solution and create a latent “negative” of theink image that is desired to be printed on a receiving substrate 34.Image areas are created where ink is desired, and non-image areas arecreated where the fountain solution remains. While the opticalpatterning subsystem 16 is shown as including laser emitter 36, itshould be understood that a variety of different systems may be used todeliver the optical energy to pattern the fountain solution layer.

Still referring to FIG. 1, a vapor vacuum 38 or air knife may bepositioned downstream the optical patterning subsystem to collectvaporized fountain solution and thus avoid leakage of excess fountainsolution into the environment. Reclaiming excess vapor prevents fountainsolution from depositing uncontrollably prior to the inking apparatus 18and imaging member 24 interface. The vapor vacuum 38 may also preventfountain solution vapor from entering the environment. Reclaimedfountain solution vapor can be condensed, filtered and reused asunderstood by a skilled artisan to help minimize the overall use offountain solution by the image forming device 10.

Following patterning of the fountain solution layer by the opticalpatterning subsystem 16, the patterned layer over the reimageablesurface 26 is presented to the inking apparatus 18. The inker apparatus18 is positioned downstream the optical patterning subsystem 16 to applya uniform layer of ink over the layer of fountain solution and thereimageable surface layer 26 of the imaging member 24. The inkingapparatus 18 may deposit the ink to the evaporated pattern representingthe imaged portions of the reimageable surface 26, while ink depositedon the unformatted portions of the fountain solution will not adherebased on a hydrophobic and/or oleophobic nature of those portions. Theinking apparatus may heat the ink before it is applied to the surface 26to lower the viscosity of the ink for better spreading into imagedportion pockets of the reimageable surface. For example, one or morerollers 40 of the inking apparatus 18 may be heated, as well understoodby a skilled artisan. Inking roller 40 is understood to have a structurefor depositing marking material onto the reimageable surface layer 26,and may include an anilox roller or an ink nozzle. Excess ink may bemetered from the inking roller 40 back to an ink container 42 of theinker apparatus 18 via a metering member 44 (e.g., doctor blade, airknife).

Although the marking material may be an ink, such as a UV-curable ink,the disclosed embodiments are not intended to be limited to such aconstruct. The ink may be a UV-curable ink or another ink that hardenswhen exposed to UV radiation. The ink may be another ink having acohesive bond that increases, for example, by increasing its viscosity.For example, the ink may be a solvent ink or aqueous ink that thickenswhen cooled and thins when heated.

Downstream the inking apparatus 18 in the printing process directionresides ink image transfer station 46 that transfers the ink image fromthe imaging member surface 26 to a print substrate 34. The transferoccurs as the substrate 34 is passed through a transfer nip 48 betweenthe imaging member 24 and an impression roller 50 such that the inkwithin the imaged portion pockets of the reimageable surface 26 isbrought into physical contact with the substrate 34.

Rheological conditioning subsystems 22 may be used to increase theviscosity of the ink at specific locations of the digital offset imageforming device 10 as desired. While not being limited to a particulartheory, rheological conditioning subsystem 22 may include a curingmechanism 52, such as a UV curing lamp (e.g., standard laser, UV laser,high powered UV LED light source), wavelength tunable photoinitiator, orother UV source, that exposes the ink to an amount of UV light (e.g., #of photons radiation) to at least partially cure the ink/coating to atacky or solid state. The curing mechanism may include various forms ofoptical or photo curing, thermal curing, electron beam curing, drying,or chemical curing. In the exemplary image forming device 10 depicted inFIG. 1, rheological conditioning subsystem 22 may be positioned adjacentthe substrate 34 downstream the ink image transfer station 46 to curethe ink image transferred to the substrate. Rheological conditioningsubsystems 22 may also be positioned adjacent the imaging member surface26 between the ink image transfer station 46 and cleaning device 20 as apreconditioner to harden any residual ink 54 for easier removal from theimaging member surface 26 that prepares the surface to repeat thedigital image forming operation.

This residual ink removal is most preferably undertaken without scrapingor wearing the imageable surface of the imaging member. Removal of suchremaining fluid residue may be accomplished through use of some form ofcleaning device 20 adjacent the surface 26 between the ink imagetransfer station 46 and the fountain solution applicator 14. Such acleaning device 20 may include at least a first cleaning member 56 suchas a sticky or tacky roller in physical contact with the imaging membersurface 26, with the sticky or tacky roller removing residual fluidmaterials (e.g., ink, fountain solution) from the surface. The sticky ortacky roller may then be brought into contact with a smooth roller (notshown) to which the residual fluids may be transferred from the stickyor tacky member, the fluids being subsequently stripped from the smoothroller by, for example, a doctor blade or other like device andcollected as waste. It is understood that the cleaning device 20 is oneof numerous types of cleaning devices and that other cleaning devicesdesigned to remove residual ink/fountain solution from the surface ofimaging member 24 are considered within the scope of the embodiments.For example, the cleaning device could include at least one roller,brush, web, belt, tacky roller, buffing wheel, etc., as well understoodby a skilled artisan.

In the image forming device 10, functions and utility provided by thedampening station 12, optical patterning subsystem 16, inking apparatus18, cleaning device 20, rheological conditioning subsystems 22, imagingmember 24 and sensor 32 may be controlled, at least in part bycontroller 60 components which are shown and described in FIG. 9 ascontroller 900. Such a controller 60 is shown in FIG. 1 and may befurther designed to receive information and instructions from aworkstation or other image input devices (e.g., computers, smart phones,laptops, tablets, kiosk) to coordinate the image formation on the printsubstrate through the various subsystems such as the dampening station12, patterning subsystem 16, inking apparatus 18, imaging member 24 andsensor 32 as discussed in greater detail below and understood by askilled artisan.

FIG. 2 shows a schematic view of a clear glass roll with internalemissive lighting system to illuminate solidified fountain solution onsurface of roller in accordance to an embodiment.

Components of the fountain measurement system 200 comprise a transferroll such as glass roll 210, emissive light 235, light detector 240, andcooler 220 for changing the phase of the transferred fountain solutionfrom surface 26 of imaging roll 24. The transfer roll is speciallyengineered to a smooth enough texture as to measure the opticalcharacteristics of the solidified fountain solution film. In thisembodiment the roller would be transparent with the capability ofallowing illumination 235 from either within or outside the rollassociated with a source driver 230 that can change the illuminationlevel of light source 235. The state of the film of fountain solution onroll 210 alters the opacity and can be varied by altering the state ofthe film. The light source 235 can include one or more light emittingdiodes (LEDs), superluminescent LEDs (SLEDs), lasers, and the like fortransmitting optical radiation (for example, light at one or morewavelengths) into roller 210 or reflecting off the surface of roller210. The system would allow this illumination to be conveyed through thesolidified film of fountain solution to a sensor (i.e. CCD) that recordsthe light transmitted through. A lower relative velocity between theimaging blanket 24 and transfer roll can be used in order to achieve theuniform film on the glass roll 210.

The fountain solution measurement 200 includes a light source 235 thatilluminates the glass roll 210 with light and a detector 240 thatreceives light passing through the glass surface from the light sourceand that generates an output signal that corresponds to receive light.As light passes through the glass roll 210 the intensity is andproportional to the thickness of the layer. When fountain solution isintroduced on the surface of glass roll 210 the intensity of thereceived light at detector 240 is attenuated. Using the well-knownBeer-Lambert law this attenuation can be expressed as a certain fractionper unit thickness.

In operation the engineered surface (glass roller) is placed near thesurface 26 of imaging blanket 24, and in Inter-document zone or anyother non-printing area of the imaging blanket, then using a heat source(LED bar or laser) to evaporate the fountain solution from the surface26 of the blanket. The roller w/ engineered surface will be at atemperature significantly cold enough for complete condensation (Vaporpressure for fountain solution is approximately 25° C.). Now that aportion or all the layer of fountain solution has been removed from theblanket and re-deposited onto the engineered roller surface, ameasurement of the amount of fountain solution on the engineered rollersurface can be obtained.

Glass roll 210 is rotated 215 at different speeds and direction ascommanded by controller 60. Additionally, the temperature of glass roll210 can be maintained or set by controller 60 using cooler 220 which maybe a physical cooling mechanism, as well as via chemical cooling. Cooler220 can be external or internal to the roll and can comprise a Peltiereffect cooling device, a coolant circulated in conduits of a coolantcirculating system, or any other suitable internally-located coolingmechanism. The glass roller with the engineered transparent surfacewould be maintained under conditions below the freezing point of thefountain solution. For fountain solution such as Cyclosiloxane,Octamethylcyclotetrasiloxane and the like this is a temperature lowerthan 17 Celsius (<17 deg C.). In this state the fountain solution wouldhave moved from being a liquid to a solid state. In its solid state thefountain solution crystalizes and changes opacity with the thickness ofthe film. One can then determine concentrated film thickness by opacityor crystallization measurement on the outer surface of roller 210.

By continuously monitoring the light 235 as it passes through the glassroll 210, the change in opacity due to the introduction ofcrystallization on the roll can be measured. Using the captured imagethe fountain solution thickness can be determined and controlled.

FIG. 3 is part of a digital image forming device that includes afeedback loop for controlling and applicator that dispenses fluidsolution in accordance to an embodiment. Apparatus comprises anapplicator for dispensing fountain solution through valve actuator 315,an fountain solution measurement with glass roll 210 and light detector240, and a controller 60. In operation, transfer the FS film fromblanket surface 26 to a transparent roller 210 where its depth can beincreased and controlled by concentrating the fountain solution film onthe well-controlled surface. Then the fountain solution on roll 210 isilluminated from one side to test for levels of opacity due to changesin the fountain solution solid based on the thickness. As noted abovewith reference to FIG. 2 changes in thickness affects the crystalstructure and changes opacity limiting the light transfer through thefountain solution and transparent roller. By analyzing the light outputto a light detector 240 like a CCD device the film thickness isdetermined. Controller 60 evaluates the CCD image for solid texture toevaluate opacity and thickness via image analysis i.e. MatLab.Controller 60 produces actionable information such as control valuesthat can be used by the dampening solution subsystem such as fountainsolution applicator 14 to increase or decrease the fountain solutionapplied to imaging blanket 24 or digital imaging member.

FIG. 4 is a block diagram of a controller with a processor for executinginstructions to automatically control devices in the digital imageforming device depicted in FIGS. 1-3 in accordance to an embodiment.

The controller 60 may be embodied within devices such as a desktopcomputer, a laptop computer, a handheld computer, an embedded processor,a handheld communication device, or another type of computing device, orthe like. The controller 60 may include a memory 320, a processor 330,input/output devices 340, a display 330 and a bus 360. The bus 360 maypermit communication and transfer of signals among the components of thecomputing device 60.

Processor 330 may include at least one conventional processor ormicroprocessor that interprets and executes instructions. The processor330 may be a general purpose processor or a special purpose integratedcircuit, such as an ASIC, and may include more than one processorsection. Additionally, the controller 60 may include a plurality ofprocessors 330.

Memory 320 may be a random access memory (RAM) or another type ofdynamic storage device that stores information and instructions forexecution by processor 330. Memory 320 may also include a read-onlymemory (ROM) which may include a conventional ROM device or another typeof static storage device that stores static information and instructionsfor processor 330. The memory 320 may be any memory device that storesdata for use by controller 60. Memory 320 maintains a multidimensionallookup table (LUT) of control values such as values correlating thefountain solution thickness to opacity or instructions for calculatingFS thickness using Beer-Lambert Law for opacity and thickness. These LUTvalues can be used to print a diagnostic print or to make adjustment tothe fountain solution to optimized control values for printing.

Input/output devices 340 (I/O devices) may include one or moreconventional input mechanisms that permit a user to input information tothe controller 60, such as a microphone, touchpad, keypad, keyboard,mouse, pen, stylus, voice recognition device, buttons, and the like, andoutput mechanisms such as one or more conventional mechanisms thatoutput information to the user, including a display, one or morespeakers, a storage medium, such as a memory, magnetic or optical disk,disk drive, a printer device, and the like, and/or interfaces for theabove. The display 330 may typically be an LCD or CRT display as used onmany conventional computing devices, or any other type of displaydevice.

The controller 60 may perform functions in response to processor 330 byexecuting sequences of instructions or instruction sets contained in acomputer-readable medium, such as, for example, memory 320. Suchinstructions may be read into memory 320 from another computer-readablemedium, such as a storage device, or from a separate device via acommunication interface, or may be downloaded from an external sourcesuch as the Internet. The controller 60 may be a stand-alone controller,such as a personal computer, or may be connected to a network such as anintranet, the Internet, and the like. Other elements may be includedwith the controller 60 as needed.

The memory 320 may store instructions that may be executed by theprocessor to perform various functions. For example, the memory maystore instructions to control the application of fountain solution,dithering and controlling the current applied to the laser so as toadjust the optical power for patterning the fountain solution on thedigital imaging member 24, and other control functions enumeratedherewith.

FIG. 5 shows transferring fountain solution by evaporation from theimaging blanket to the clear glass roll for fountain solutionmeasurement in accordance to an embodiment illustrated is a method oftransferring fountain solution 25 to glass roll 210, which forms part ofthe fountain measurement system 200, through evaporation andre-condensation. After transferring of the fountain solution measurementsystem 200 in cooperation with light, detector, and controller measuresthe thickness by monitoring the change of opacity of the glass roll 210.

The original fountain solution 25 is heated to evaporation 510 in closeproximity of the transfer roll/member 210, which is kept at lowtemperature. The vapor will quickly re-condense 520 on the transfer rollsurface of 210 where fountain measurement system 200 uses opticalproperties of solidified fountain solution film to determine thickness.Subsequent film thickness measurement can be performed on the glass rollsurface using an emissive light, detector, and controller like shown inFIG. 2. It should be noted, in this process ofevaporation/re-condensation transfer, the transfer member 210 canoperate in either direction. Additionally, the speed of the transfermember 210 can be significantly different from that of the originalfountain solution carrier like imaging blanket 24. With variable speedand direction 215 would provide the opportunity to concentrate/thickenthe fountain solution on the transfer roll 210. For example, one can runthe transfer roll at 1/10 the speed of the blanket 24. The fountainsolution on the transfer member 210 will then be much thicker for easiermeasurements. Of course, one could also run the transfer roll 210 fasterto obtain a thinner film if desired. Being able to thicken and thin thefilm during transfer can greatly enhance the dynamic range of themeasurement system.

FIG. 6 is a plot of opacity as a function of thickness of the solidifiedfountain solution in accordance to an embodiment. Opacity transferfunction 600 shows the relationship between fountain solution thickness610 as function opacity 620 on a glass such as glass roll 210. In theplot opacity 620 represents length of glass—measured in pixels withthickness increasing from left to right. The transfer function 600 showsa spike 640 created by clamps which secured the glass structure fortesting. The transfer function is consistent with Beer-Lambert Law andthe relationship of penetration depth that measures how deep light orany electromagnetic radiation can penetrate fountain solution on thesurface of glass roll 210.

FIG. 7 is a flowchart depicting the operation of an exemplary method todirectly measure fountain solution for use in a digital image formingdevice. Method 700 begins with action 710 when the system or operatorinvokes a fountain solution measurement routine at lithography system 10of FIG. 1. In action 710, method 700 illuminates engineered surfaceusing emissive light source like described in FIG. 2. In action 720, themethod 700 receives light passing through engineered surface using alight detector. In action 730, the method 700 generates output signalsthat correspond to the opacity level of the engineered surface likeshown in FIG. 6. In action 740, method 700 determines fountain solutionthickness (FST) from the opacity level of the engineered surface.Actions 750 and 760 are of importance when image forming 10 is beingcontrolled to maintain and/or achieve a certain level of fountainsolution thickness. In action 750, method 700 checks to see if thedetermined fountain solution thickness is within a certain range. Therange should be between 48 to 52 nanometers (nm) with roughly estimatedthickness around 50 nm to prevent ink from developing in the backgroundto maintain image quality. If FST is within range then control is action710 to continue to monitor the thickness of the fountain solution.However, if FST is not in range then control is passed to action 760where a control signal is send to the fountain solution depositionprocess to increase or decrease the fountain solution by an amountproportional to the deviation from the range.

Those skilled in the art will appreciate that other embodiments of thedisclosed subject matter may be practiced with many types of imageforming elements common to offset inking system in many differentconfigurations. For example, although digital lithographic systems andmethods are shown in the discussed embodiments, the examples may applyto analog image forming systems and methods, including analog offsetinking systems and methods. It should be understood that these arenon-limiting examples of the variations that may be undertaken accordingto the disclosed schemes. In other words, no particular limitingconfiguration is to be implied from the above description and theaccompanying drawings.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art.

What is claimed is:
 1. A method to measure fountain solution thicknessfor variable data lithography printing comprising: transferring fountainsolution from an imaging member onto an engineered surface byevaporating the fountain solution on the imaging member andre-condensing on the engineered surface, the engineered surface havingan opacity that varies as a function of fountain solution thickness;using an emissive light source to pass a light along a path from thesource through the engineered surface; receiving light passing throughthe engineered surface at a light detector; generating a signalproportional to the opacity level of the engineered surface from thelight impinging on the light detector; and determining the thickness ofthe fountain solution on the engineered surface from the opacity level.2. The method in accordance to claim 1, wherein the light source and thelight detector are positioned on respective opposite portions of theengineered surface.
 3. The method according to claim 2, wherein thelight detector records the light transmitted through the engineeredsurface.
 4. The method according to claim 3, wherein the engineeredsurface is a clear glass roll.
 5. The method according to claim 4,wherein the emissive light source is contained within the clear glassroll.
 6. The method in accordance to claim 1, further comprisingcontrolling the fountain solution deposition process based on thedetermined thickness of the fountain solution.
 7. A method to measurefountain solution thickness for variable data lithography printingcomprising: using an engineered surface with an opacity that varies as afunction of fountain solution thickness; using an emissive light sourceto pass a light along a path from the source through the engineeredsurface; receiving light passing through the engineered surface at thelight detector; generating a signal proportional to the opacity level ofthe engineered surface from the light impinging on the light detector;and determining the thickness of the fountain solution on the engineeredsurface from the opacity level, the method further comprising coolingthe engineered surface to phase change the fountain solution to a solid.8. The method in accordance to claim 7, the method further comprising:applying a layer of fountain solution to an imaging member having anarbitrarily reimageable imaging surface.
 9. The method in accordance toclaim 8, the method further comprising: transferring a portion of thefountain solution on the imaging member onto the engineered surface. 10.The method in accordance to claim 9, wherein the transferring includesevaporating the fountain solution on the imaging member and depositionon the engineered surface.
 11. The method according to claim 10, whereinthe determining the thickness of the fountain solution is evaluating animage for solid texture to evaluate opacity and thickness via imageanalysis.
 12. An ink-based digital printing system useful for inkprinting, comprising: a processor; and a storage device coupled to theprocessor, wherein the storage device comprises instructions which, whenexecuted by the processor, cause the processor to control fountainsolution deposition process and maintain fountain solution at a setthickness for variable data lithography printing by: using an engineeredsurface with an opacity that varies as a function of fountain solutionthickness; using an emissive light source to pass a light along a pathfrom the source through the engineered surface; receiving light passingthrough the engineered surface at a light detector; generating a signalproportional to the opacity level of the engineered surface from thelight impinging on the light detector; determining the thickness of thefountain solution on the engineered surface from the opacity level; andcontrolling the fountain solution deposition process based on thedetermined thickness of the fountain solution, the processor furtherperforming cooling the engineered surface to phase change the fountainsolution to a solid.
 13. The ink-based digital printing system inaccordance to claim 12, wherein the light source and the light detectorare positioned on respective opposite portions of the engineeredsurface.
 14. The ink-based digital printing system according to claim13, wherein the light detector records the light transmitted through theengineered surface.
 15. The ink-based digital printing system accordingto claim 14, wherein the engineered surface is a clear glass roll. 16.The ink-based digital printing system according to claim 15, wherein theemissive light source is contained within the clear glass roll.
 17. Theink-based digital printing system in accordance to claim 13, theprocessor further performing: applying a layer of fountain solution toan imaging member having an arbitrarily reimageable imaging surface. 18.The ink-based digital printing system in accordance to claim 17, theprocessor further performing: transferring a portion of the fountainsolution on the imaging member onto the engineered surface.
 19. Theink-based digital printing system in accordance to claim 18, wherein thetransferring is evaporating the fountain solution on the imaging memberand re-condensing on the engineered surface.
 20. The ink-based digitalprinting system according to claim 19, wherein the determining thethickness of the fountain solution is evaluating an image for solidtexture to evaluate opacity and thickness via image analysis.